HP 8340B Manual page 271

RPG
Rotating the
RPG (rotary pulse generator) increments or decrements
a
counter, and generates
a service request,
with the main instrument microprocessor reading the counter output.
POWER STANDBY/ON SWITCH
The front panel power standby/on switch is an open circuit in the on position. In
standby,
a
ground
is supplied to
the yellow standby LED, and to the fan relay. This ground
is
also LSBY (low standby).
In
standby, the
fan relay
is
energized,
and the power to the fan is
removed. The LSBY signal
is fed
to the
+20V
regulator, which shuts down the
+20V
supply. Because the
+20V
supply
is
a
reference for
all
other regulated
supplies,
all
regulated supplies are shut down as
well.
In
the standby mode,
line
power
is still
applied to
the
power transformer primary and to the unregulated supplies.
A1
ALPHA DISPLAY ASSEMBLY
The
A1
alpha display assembly provides the physical mounting for the seven 4-character dot matrix display
elements. The assembly
is mounted on the front panel bezel, and interfaces
to the
A2 display driver assembly via
a
multi-pin
connector.
A2 DISPLAY DRIVER ASSEMBLY
The A2
display driver assembly contains the
7-segment
displays and the instrument annunciators, and
it
pro¬
vides an interface with the
A1 alpha display assembly.
A3 DISPLAY PROCESSOR ASSEMBLY
The A3 display
processor assembly
provides the communication link for Interfacing the main instrument micro¬
processor to the instrument displays. The instrument microprocessor sends display data to the
A3
display
processor via the instrument data and address busses. The A3 display processor stores the data in
internal
RAM
(random access memory), and processes the data into the necessary control signals to display the information.
The display processor has 2K of internal ROM (read
only memory) that contains the program for display control.
The A3 display
processor assembly outputs
control signals to the A2 display driver assembly for the
power/
frequency 7-segment
displays, the entry display 5X7 dot matrix displays, and the instrument LED annunciators.
HP 8340B/41B
Front Panel Theory of Operation G-3